The present invention relates to a classifier used in cement manufacturing facilities and the like.
FIGS. 1 and 2 show a conventional classifier. In the figures, reference numeral 1 denotes a classifier casing which comprises an upper cylindrical casing section 4 having a raw material inlet 3 for receiving a raw material 2 in a position on an upper surface of the section 4 and a lower funnel-shaped casing section 5 contiguous with a lower portion of the section 4 and having its diameter gradually reduced downwardly.
A vortex chamber 7 with a plurality of louvers 6 annularly arranged on an inner periphery of the chamber 7 is formed on and is protruded outwardly from a lower portion of the lower casing section 5. A classifying air introduction pipe 8 opened to the chamber 7 is arranged tangentially on an outer periphery of the chamber 7 (see FIG. 2).
Under the vortex chamber 7, the lower casing section 5 has a lower crude powder outlet 10 for discharging crude powder 9 falling along an inner surface of the lower casing section 5.
Reference numeral 11 designates a separator main body which is driven by a drive 12 on the upper surface of the upper casing section 4 and which is supported from above by a rotary shaft 13 rotatably supported substantially at a center of the section 4. The separator main body 11 comprises a mounting plate 15 fixed to a lower end of the rotary shaft 13, a dispersion plate 16 fixed to an upper portion of the shaft 13 to receive the raw material 2 from the inlet 3 and classifying blades 17 arranged peripherally along an outer periphery of the plate 15 and fixed between the plates 15 and 16.
Reference numeral 18 represents a fine powder hopper arranged under the separator main body 11. The fine powder hopper 18 comprises a funnel-shaped hopper main body 19 having its diameter gradually reduced downwardly and an exhaust outlet 22 extending from a lower end of the hopper main body 19 through the lower casing section 5 to outside of the section 5 so that fine powder 20 introduced via the classifying blades 17 into the separator main body 11 can be discharged outside together with classifying air 21.
When the drive 12 is actuated to rotate the separator main body 11 via the rotary shaft 13 and at the same time the classifying air 21 is introduced from the introduction pipe 8 into the vortex chamber 7 and the raw material 2 is charged by a predetermined quantity into the casing 1 through the inlet 3 on the upper surface of the casing 1, the raw material 2 thus charged falls onto the rotating dispersion plate 16 so that, with centrifugal force being given to the raw material 2, the raw material 2 is dispersed peripherally outwardly of the plate 16.
In this case, the classifying air 21 from the introduction pipe 8 into the vortex chamber 7 is given swirling force by the chamber 7 and flows into the casing 1 through the louvers 6. Thus, a flow of classifying air 21 is provided which swirls up along the inner surface of the lower casing section 5 and flows into the rotating separator main body 11 through the classifying blades 17, so that the raw material 2 falling from above onto the dispersion plate 16 is dispersed into the flow of the classifying air 21.
The raw material 2 entrained on the flow of the classifying air 21 is classified into fine and crude powders 20 and 9, the fine powder 20 being the powder which is allowed to pass through the classifying blades 17 while the crude powder 9 is the powder which is not allowed to pass. Only the fine powder 20 allowed to pass through the classifying blades 17 is guided into the separator main body 11, flows down into the hopper main body 19 of the fine powder hopper 18 and is discharged outside together with the classifying air 21 through the exhaust outlet 22.
On the other hand, the crude powder 9 which is not allowed to pass through the classifying blades 17 and is flapped onto the inner surface of the casing 1 as well as the crude powder 9 which cannot be entrained on the flow of the classifying air 21 from the beginning are away from the flow of the classifying air 21, fall down along the inner surface of the casing 1 and are discharged outside through the lower outlet 10.
In such classifier, number of revolutions of the separator main body 11 required for classification of the raw material 2 will depend on particle size distribution of the raw material 2 to be classified and is usually in a range of 100 to 1000 r.p.m. Number of revolutions of the dispersion plate 16 required for dispersion of the raw material 2 will depend on diameter of the dispersion plate 16 and amount of raw material to be supplied and is usually on the order of 10 to 100 r.p.m.
However, in the conventional classifier as shown in FIGS. 1 and 2, the dispersion plate 16, which is integrated with the separator main body 1, is rotated at the rotating speed of the separator main body 11 required for classification. As a result, the raw material which falls onto the dispersion plate 16 is scattered with centrifugal force higher than required; therefore, most of the raw material 2, which is to be entrained on the flow of the classifying air 21 and transported to the classifying blades 17 of the separator main body 11, will violently strike on and fall along the inner surface of the casing 1 without fully entrained on the flow of the classifying air 21, resulting in discharge of most of the powder as crude powder 9 without having an enough chance for classification, which disadvantageously leads to lowering of classifying efficiency. Because more quantity of powder strikes on and falls along the inner surface of the casing 1, the inner surface of the casing 1 tends to be worn out.
The present invention was made in view of the above and has its object to provide a classifier capable of preventing a centrifugal force more than required from being given to raw material to be dispersed by a dispersion plate.